The invention relates to control for the automatic locking of the transfer case of a motor vehicle equipped with a multi-axle drive as a function of the steering angle and the driving speed of the motor vehicle for example. This type of arrangement is known from DE-OS 35 05 455and corresponding U.S. Pat. No. 4,681,185. It concerns a vehicle having a multi-axle drive with a transfer transmission and locks for the transfer transmission and for the differential gears. In this case, the connecting of the transfer transmission and of the locks takes place automatically as a function of several criteria which characterizes the moving condition of the vehicle and include steering angle and driving speed. Among the criterion for example, is a reference quantity of the rotational speeds of the wheels of one axle.
In the technical field of drives, concepts that have a multi-axle drive are known to be very efficient. A disadvantage in the case of low adhesion coefficients is a spinning of the wheels which results in a loss of lateral control and impairs the driving stability considerably. As a remedy, a wheel slip control of all driven wheels is known and corresponding U.S. patent application Ser. No. 912,321 (DE-OS 35 34 443). This is very effective but also very costly. It is the objective of the present invention to provide for the known, very costly combination of the multi-axle drive and a wheel slip control of all driven wheels an alternative solution that is just as effective but much less costly.
According to the invention, this objective is achieved by a control for the lock of a transfer transmission on an automatic vehicle with multiple axle drive using both the lock control signal generated as a function of steering angle and drive speed as well as the control signal from the antislip system. A logic is provided for providing the locking control when either a lock control signal is generated by the standard transfer transmission control lock system or by the control signal of the antislip system. The antislip system output control generally include a brake torque control and an engine torque control signal. As a result, at least the costly differential gear locks and the electronic control system and the hydraulic brake system of the wheel slip control can be saved for the wheels of one axle. In addition, only one brake circuit must be connected with one pressure reservoir. The connecting of the transfer transmission lock, in addition, has advantages with respect to driving dynamics that apply particularly in the case of obstacle-avoidance maneuvers or when driving turns in the case of low adhesion coefficients.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.